what is the meaning of this std::string constructor

Question

Today I tried to study some piece of code and I am stuck with this line.

std::vector<std::string(SomeClassInterface::*)()> ListOfFnPointers;

what is the meaning of this std::string constructor? I went through this but I have no idea what it means.

It is used in the code as,

if (!ListOfFnPointers.empty())
{
    std::vector<std::string> StringList;
    for (auto Fn : ListOfFnPointers)
    {
        StringList.push_back((pSomeClassObj->*Fn)());
    }
    ...
}

1. What that declaration means?
2. what exactly this function doing with pSomeClassObj->*Fn?

Answer 1

It has nothing to do with std::string constructor.

std::string(SomeClassInterface::*)() is type of pointer to member function, the member function belongs to class SomeClassInterface, returns std::string, takes no parameters.

->* is pointer-to-member access operator (and also .*). (pSomeClassObj->*Fn)() will call the member function on pSomeClassObj, which is supposed to be a pointer with type SomeClassInterface*.

Answer 2

It's not a constructor it's a pointer to function without parameters returning std::string.

for (auto Fn : ListOfFnPointers)
{
    StringList.push_back((pSomeClassObj->*Fn)());
}

Push back's above are working because (pSomeClassObj->*Fn)() is a call to these functions and result is std::string.

UPDATED:

1. It is declaration of std::vector of pointers to function. Each function belongs to SomeClassInterface, takes no parameters and return std::string.

2. In case of this code (pSomeClassObj->*Fn)() calls the function of objects pSomeClassObj where Fn is a pointer to this function and member of pSomeClassObj.

Answer 3

If you use C++11,you can write code like this:

using FunctionPointer = std::string (SomeClassInterface::*) ();
std::vector<FunctionPointer> ListOfFnPointers;

you can read this link: http://en.cppreference.com/w/cpp/language/type_alias